Post #1677760
2026-04-23 22:56 UTC
@rtn Hehe. It's one of those problems that tempts you to use System 1 (quick) brain, but requires System 2 (slow) brain.
Speed = Distance / Time = D / T
Given D / T = 50 km/hr
Given D / (T/2) = 100 km/hr
AvgSpeed = 2D / (T+T/2)
Let D = 50 km
So, T = 1 hr
AvgSpeed = 2(50) / (1 + 1/2)
AvgSpeed = 100 / 1.5
AvgSpeed = 66.6̅ km/hr
Replies (1)
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@rtn@chaos.social 2026-04-24 06:57
@tty Yep! The result is somewhat counterintuitive to me though. I feel it should be 75%.